Recovery of naphthalene



De. 7, 1943. Z `J HAPPEL 2,336,244

' RECOVERY oF NAPHTHALENE Filed Feb. '7, 1939 @ggf H547' g/ H?? X0/ANGE?A r CENTR/F065 f TRAP TRAY Ra z/x TRAP 77M y men ax T0 `sms/aff? Pan/PINVENTOR f \]0/2 Ha/aal ATTORN Patented Dec. 7, 1943 UNITED STATESPATENT OFFICE John Happel, Brooklyn, N. Vacuum Oil Company,

N. Y., a corporation of Application February 7, l1939, 'Serial No.255,040

1 Claim.

bons such as benzene and naphthalene may be formed by subjectingpetroleum oils to thermal cracking at very high temperatures. Forinstance, Ellis ln Chemistry of Petroleum Derivatives (1934) pages 161and 162, outlined the prior art on this subject by stating that ingeneral (1) Temperatures from 500 to about 600 C. yield principallymixtures of olene and parafin hydrocarbons; (2) at about 650 C. andabove dlolenes are formed; and (3) at 700 C. and slightly above,aromatic hydrocarbons are produced in quantity." It has been theprevailing opinion throughout the art that in order to produce aromaticssuch as benzene or naphthalene, temperatures around 600 to '100 C. mustbe used, and at temperatures of conventional liquid phase cracking forgasoline, i. e., temperatures below 1000 F. (538 C.) such aromaticcompounds are not formed at all.

My invention is based upon the discovery that naphthalene is produced inappreciable quantities` under certain conditions during the cracking ofpetroleum oils 4to gasoline at temperatures below 1000 F. Thus contraryto the prior knowledge nf the art. I have found that in the conventionalgasoline liquid phase cracking of petroleum oils Tree of naphthalene attemperatures below 1000 .,.e. g., 800 F., to 1000 F., an appreciablequanity of naphthalene is formed and as a result oi' ts boiling pointnormally tends to accumulate in yhe recycle stock. According to myinvention a uitable fraction' or the cracked product, e. g., the `ecyclestock for the cracking operation or a rap tray redux/,from the bubbletower, which vould contain the naphthalene is subjected to a ecoveryprocess for the naphthalene.

The recovery of the naphthalene from the tream containing it may beeffected continously or intermittently since the naphthalene ierelyaccumulates in the cycle stocks if not reloved at once. thereby causingthe concentra-1 on to increase as the cracking progresses. The

Y., assignor to Soconyi Incorporated, New York,

New York reason for this is because the pressure still tar does notcontain large percentages of fractions boiling as low as naphthalene(424 F.) and, ifl

proper fractionation is applied to the separation of the gasoline, allnaphthalene will remain in the cycle stocks and its concentrationincrease since naphthalene is more refractory than the bulk of cyclestock. The amount of naphthalene that is recovered varies with thecharging stock. cracking conditions, length of run, etc. In a cyclestock from cracking Mid-Continent gas oil at 960-967 F. transfer linetemperature and 790 lbs./sq. in pressure. the concentration ofnaphthalene was 0.36 lb./bbl. of cycle stock after three days ofoperation.

Accordingly, my invention based upon my discovery that naphthaleneoccurs in the cycle stocks of gasoline cracking processes affords avaluable new by-product for such processes that may be easilyrecovered.'v The recovery isV preferably accomplished by suitablecooling to precipitate the naphthalene and then removing theprecipitated naphthalene by ltering or centrifuging.- It is desirable ofcourse to utilize as much heat as possible in cooling by suitable heatexchange. The temperature to which the stream must be cooled in order toprecipitate the naphthalene will vary depending upon the composition ofthe' C. or lower stream. Temperatures as low as 20 may have to be usedin some cases, whilein other instances precipitating temperaturesconsider-f ably higher, e. g., +32 F. may be adequate.

The invention will be further described with reference to theaccompanying drawing wherein Figure 1 is a flow diagram of a typicalrecovery system for the naphthalene that may be applied to anynaphthalene-containing stream, and

Figure 2 is a ow o manner of recovering thenaphthalene from the traptray reflux leaving the bubble tower of a cracking unit.

Referring to Figure l, a suitable stream of the renery such as therecycle stock or bubble tower trap tray reflux containing naphthalene iscooled by passing through heat exchanger l in indirect heat exchangewith the cool stream after re moval of naphthalene. From exchanger l thestream containing naphthalene passes to refrigerator 2 wherein it iscooled sulllciently to precipitate the naphthalene and then the streamis passedto filter or centrifuge 3 wherein the precipitatednaphthalenels separated. The cool naphthalene-free stream is then sentthrough exchanger l to whatever use it is to be put.

In Figure 2 the trap tray reflux is drawn o ,diagram showing a preferredfrom bubble tower 4 at about 424 F.. and is used to heat the reboiler 6o! a stabilizer tower (not shown). From the reboiler B the reflux passesthrough a suitable water cooler 6. On leaving cooler 6 the redux passesthrough a. naphthalene recovery system similar to that shown in Figure1, comprising heat exchanger I, refrigerator 2, and filter or centrifuge3.. The cool naphthalenetree reiiux leaving filter I is pumped backthrough heat exchanger I to the top of bubble tower 4.

I claim:

The process of producing naphthalene which comprisesfcracking va,charging stock consisting only or Mid-Continent gas oil in liquid phaseto gasoline under cracking conditions in the absence oi added ,hydrogenat a' temperature between about 800 and 1000 F., separating crackedproduct into gasoline, recycle, and residuum fractions, cooling therecycle stock fraction until naphthalene contained therein isprecipitated, and then recovering said precipitated naphthalene prior torecharging the recycle fraction to the cracking operation.

JOHN RAPPEL.

